1. Field of the Invention
This invention relates in general to gate valves, and in particular to an improved metal-to-metal seal for sealing between a movable stem and a stem opening in a valve body.
2. Description of the Prior Art
A typical gate valve has a body with a flow passage extending through it. The flow passage intersects a central cavity wherein is located a gate that is perpendicular to the flow passage. In communication with the central cavity is a stem opening. A stem extends through the stem opening and into the central passage where the stem is connected to the gate. Selective movement of the stem causes the gate to move between closed and open positions that obstruct flow or allow flow, respectively, through the flow passage.
There are generally two types of gate valves: the rising-stem type, and the non-rising-stem type in the rising-stem type, the stem moves only axially without rotation, to move the gate between closed and open positions. In the non-rising-stem type, the stem only rotates, without moving axially, and the rotation of the stem, in conjunction with a gear connection between the stem and the gate, causes the gate to move between open and closed position.
Since the central cavity of the gate valve and the stem opening are in communication, the space between the stem and the stem opening must be sealed to avoid leakage. At first, elastomeric seals were used. However, since elastomeric seals do not have the necessary longevity, especially in corrosive environments, metal seals have become popular for several applications.
Several metal-to-metal seals have been developed for sealing between a movable stem and a stem opening in a valve body. However, generally such seals made prior to this invention have disadvantages such as premature wear, damage to the sealing surface, insufficient sealing capacity under certain conditions, and excessively short service life.